INTERACTION BETWEEN SULPHITES AND NITRITES. 301 



tioii of all carbonate locally present to acid carbonate and 

 sulphite has been effected. Then the reaction that ensues is — 



NaNOs + NaHCOs + 2S0, = Na.H NS,0, + CO, 

 When all normal carbonate in the solution has been acidified by 

 the carbon dioxide, the sulphite becomes as active as the acid 

 carbonate and neither salt gets consumed before the other. 



While it seems certain that first the sulphur dioxide converts 

 the normal carbonate into normal sulphite and acid carbonate, 

 and only then produces hydroximidosulphate by acting on the 

 nitrite along with acid carbonate in the earlier stages and on 

 both this and normal sulphite collaterally in the later stages, the 

 experimental results show that local saturation must take place 

 largely where the sulphur dioxide enters the solution, since so 

 much sulphonate is produced along with the sulphite. In con- 

 sequence of the activity of acid carbonate, local saturation be- 

 comes twice as difficult to prevent as when hydroxide is used 

 in place of carbonate. 



If in order to impede local saturation we slacken the rate 

 of passage of the sulphur dioxide into the solution, we meet with 

 a good amount of success. Thus, it was shown by the results of 

 experiments already given, that the slower rate gave proportion- 

 ately less sulphonate and more sulphite. But the effect of 

 slowness in passing in the gas has its limit, in consequence of 

 the continuous though slow interaction which takes place between 

 nitrite, normal sulphite, and acid carbonate whereby sulphite 

 disappears to give place to sulphonate. It follows that too slow 

 as well as too rapid an addition of sulphur dioxide is unfavour- 

 able to the accumulation of sulphite, rather than of sulphonate, 

 in the solution, and that a medium rate of supply is best for 

 raising the proportion of sul[)hite. 



